The long-term objective of this proposal is to understand the role of muscle caveolae and caveolin-3 i) in normal muscle development; and ii) in the pathogenesis of muscle dystrophy. Caveolae are "little caves" at the surface of cells. It has been proposed that caveolae function as message centers" for regulating signal transduction. Caveolin-3, a muscle-specific caveolin-related protein, is the principal structural protein of caveolae membrane domains in striated muscle cell types (cardiac and skeletal). Recently, we identified a novel autosomal dominant form of limb girdle muscular dystrophy (LGMD-1C) in humans that is due to mutations within the coding sequence of the human caveolin-3 gene (3p25). The aim of this proposal is to test the hypothesis that caveolin-3 expression is important for normal muscle development and that changes in caveolin-3 expression (either up-regulation or down-regulation) can result in muscular dystrophy phenotype. In order to test this hypothesis,, we will use a variety of complementary in vivo approaches, such as the use of caveolin-3 anti-senses in cultured cells and the development of mouse animal models. The specific aims of the project are: 1) To determine the role of caveolin-3 mutations in the pathogenesis of LGMD- 1C. We will examine the phenotypic behavior of LGMD-1C mutations of caveolin-3 after heterologous expression in NIH 3T3 cells, as compared with wild-type caveolin-3; 2) To develop transgenic mouse models that over wild-type caveolin-3 and LGMD-1C mutant forms of caveolin-3. We will over-express wild type and LGMD-1C mutant forms of caveolin- 3 as transgenes in mice and assess their effects on skeletal muscle. As caveolin-3 levels are up-regulated in Duchenne's muscular dystrophy, these experiments will help us evaluate if caveolin-3 up-regulation contributes to the pathogenesis of this diseases; and 3) To examine if caveolin-3 expression is required for normal muscle development. Using an anti-sense approach, we will abrogate caveolin-3 expression in C2C12 cells, a skeletal myoblast cell line that differentiates in culture. We will then assess the effects of caveolin-3 down-regulation on C2C12 myoblast fusion and myotube formation. In addition, through a targeted gene disruption approach, we will create and characterize "knock-out" mice that lack caveolin-3 gene expression. It is expected that these studies will contribute fundamen6tal knowledge toward understanding the role of muscle cell caveolae in normal muscle development and muscular dystrophy.